How can you accurately measure flow using ultrasonic flow meters?

The sending ultrasonic waves across a pipe, containing the flow in the direction of the flow and in the opposite direction of the flow. The ultrasonic waves and the velocity of the flow of the liquid can be combined to determine the flow rate. There are 3 methods in Ultrasonic flow measurement technology 1)Transit time Method 2)Doppler Method 3) Open channel Method - In Open channel ultrasonic element is actually measuring the height of the water in the open channel Ultrasonic Flow measurement cannot be used for heavily contaminated liquids.

Ultrasonic flow meters measure flow by using ultrasonic sound waves transmitted through a fluid. They employ either the transit-time or Doppler method. Transit-time method: This involves sending ultrasonic pulses upstream and downstream in the flow. The difference in time it takes for the pulses to travel in each direction is used to calculate the flow rate. This method is suitable for fluids with little or no particulates. Doppler method: Doppler ultrasonic flow meters measure the frequency shift of reflected sound waves off moving particles or bubbles within the fluid. The change in frequency is used to calculate flow velocity. This method is useful for fluids containing particles or bubbles.

there is two types of UFM working princibles as followes: 1- Doppler Principle When sound of a given frequency reflects off a moving object, the reflected frequency is shifted in proportion to the velocity of the moving object. Therefore, Doppler meters require the presence of a second phase or “object” in the flow stream in order to make a measurement. unfortunately this tech. is not commonly used because of the accuracy and some points related to Scatterer Size...etc 2- Transit time Transit-time flow meters use two or more transducers that alternately send and receive signals along and against the flow direction. The difference in transit time between the signals is proportional to the average fluid velocity

Nowadays the ultrasonics meters has a wide range of applications, since the most small for pumping towers in labs of Pharma industry’s until big sizes in Oil and Gas, but that’s doesn’t mean one technology fits all applications in between. Most of meters were designed for some applications, in others works well and in there are some which doesn’t fit or could be some expensive for them.

The following factors affect the performance of ultrasonic flow meters. 1- Surface Condition 2- Transducer Positioning/Alignment, 3- Calibration. 4- Taper or Eccentricity 5- Acoustic Properties of the Material 6- Process Conditions (T,P...etc)

Also consider 1. Pipe or tube thickness and diameter of which must be calculated and put in the menu setup settings. 2. Be sure that the temperature of the fluid doesn't change as that will affect the viscosity of the product being measured. 3. There must not be a mix product as that will affect the flow reading's accuracy.

May I add that temperature compensation is often not given enough consideration. Ultrasonic sensors are extremely sensitive to ambient air temperature and will give erroneous results unless properly compensated. Always include a vendor certification requirement in the vendor document requirements list covering the operating ambient temperature of the meter. This is especially important for clamp on meters.

Accurate placement of the transducer is the key to accuracy of the flow meters reading. The principal key of the process is the refraction angle of the ultrasonic signal as it passes through the pipe.

Several factors impact accurate ultrasonic flow measurement: calibration for precise readings, proper sensor placement in a disturbance-free section of the pipe, understanding fluid characteristics like temperature and viscosity, considering pipe condition and potential signal obstructions, and ensuring correct installation techniques and signal quality. Addressing these factors optimizes the accuracy and reliability of ultrasonic flow measurements.

Factor that also contributed to ultrasonic sensor accuracy is the bubbles and particle in the media. Bubbles and particles will interrupt the Doppler effect thus destroy the sound wave. In serious case even stop the ultrasonic flow sensor from fuctioning.

In the ten years that I have been working in the aqueduct, one of the main factors that affect the accuracy is the condition of the pipes. Normally the flow meter is configured with the thicknesses indicated by the pipe manufacturer, but in old pipes there are sediment incrustations and/or internal erosion, to minimize this problem we use pipe thickness gauges

The (7) Key Diagnostics: • Transit Time • Delta T • Sound speed • Signal Strength / Signal To Noise Ratio – SNR • Signal Quality • Peak # • Amplitude Discriminator

Ultrasonic flow meter installation itself is critical in the measurement accuracy. Since it is dependent on the distance of the sensors and its orientation. It is recommended to install them in horizontal pipes where noise disturbances are minimal. Proper grounding is also very important. Depending on the type of fluid being measured, ease of cleaning the probes and access for general maintenance should be considered. As mentioned in the article, due care must be given to installation design. This way accuracy of flow measurement can be ensured.

There are Two major sub-types of ultrasonic flowmeters exist: 1-Doppler. 2-Transit-time. Both types of ultrasonic flowmeter work by transmitting a high-frequency sound wave into the fluid stream and analyzing the received pulse. Arequirement for reliable operation of a transit-time ultrasonic flowmeter is that the process fluid must be free from gas bubbles or solid particles which might scatter or obstruct the sound waves. Note that this is precisely the opposite requirement of Doppler ultrasonic flowmeters, which require bubbles or particles to reflect sound waves. These opposing requirements neatly distinguish applications suitable for transit-time flowmeters from applications suitable for Doppler flowmeters.

Vendors' recommendations in terms of required number of pipeline diameters upstream and downstream from the FT installation point should be accounted to ensure correct measurement.

Selecting right location for installation of a flowmeter is very crucial. You must ensure sufficient upstream and downstream clear length is available. You have to ensure that the flow is laminar at the location of the meter installation.

Please also make sure the pipe is full when installing the sensors. A non-full pipe air gap is a blocker for ultrasonic waves.